The present invention is a process for the organooxylation of .beta.-cyanoalkylchlorosilanes. The process comprises contacting in a film a .beta.-cyanoalkylchlorosilane with an alcohol capable of forming an ester with the silicon of the .beta.-cyanoalkylchlorosilane and thereby forming an equilibrium mixture comprising a (.beta.-cyanoalkyl)organooxysilane and hydrogen chloride. The thin film is heated at a temperature sufficient to cause vaporization of the hydrogen chloride from the equilibrium mixture thereby increasing yield of (.beta.-cyanoalkyl)organooxysilane in the equilibrium mixture. In a preferred process, the process is run in a falling-film type reactor or a wiped-film type reactor.
The (.beta.-cyanoalkyl)organooxysilanes prepared by the present process are useful intermediates in the production of other silanes and for the production of polyorganosiloxanes containing the beta-cyanoalkyl substituent. The silicon-bond beta-cyanoalkyl radical is resistant to hydrolysis and can provide a means by which amine containing silanes and siloxanes can be formed.
The reaction of an alcohol with a .beta.-cyanoalkylchlorosilane to form a (.beta.-cyanoalkyl)organooxysilane is an equilibrium reaction exemplified by the following equation: EQU .tbd.Si--Cl+ROH.revreaction..tbd.SiOR+HCl
Therefore, to drive the reaction to favor high yields of the (.beta.-cyanoalkyl)organooxysilane it is desirable to remove the hydrogen chloride as it is formed from the reaction mixture. In addition the hydrogen chloride liberated during the reaction can attack the starting materials and products to produce undesirable by-products which also lowers the yield of the desired products. For example, liberated hydrogen chloride can react with alcohol to produce a hydrocarbon chloride and water. This results in the loss of considerable alcohol. Furthermore, water formed by this side reaction can hydrolyze the chlorosilane producing undesirable polysiloxanes and generating more hydrogen chloride. In addition to these side reaction, those skilled in the art recognize that hydrogen chloride in combination with alcohol can readily convert cyanoalkyl radicals to carbalkoxyalkyl radicals. As a result there also can be produced during the organooxylation of .beta.-cyanoalkylchlorosilanes up to 10 mole percent or more of the corresponding carbalkoxyalkylalkoxysilane. A build-up in this ester concentration can make the (.beta.-cyanoalkyl)organooxysilane unsuitable as an intermediate for various applications. Removal of such esters from (.beta.-cyanoalkyl)organooxysilane products by standard methods is difficult since the ester has a similar boiling point.
Therefore, it is an objective of the present invention to provide a process where hydrogen chloride liberated during the process is rapidly and effectively removed from the reaction mixture. The present inventors have found that this objective can be achieved by running the described equilibrium reaction in a thin-film process. The present process provides an effective means for removing reaction-liberated hydrogen chloride from the process and thereby shifting the chemical equilibrium of the process to favor production of (.beta.-cyanoalkyl)organooxysilanes and also a means for minimizing side reactions and undesired by-products as a result of these side reactions. It is furthermore an objective of the present invention to provide a process with improved mass transfer thereby allowing for more efficient reactor operation than is achieved with reactive-distillation type reactors in which the reaction is typically conducted on a commercial scale.
Schubert, U.S. Pat. No. 3,008,975, issued Nov. 14, 1961, describes a stirred-batch process for alkoxylating chlorosilanes with an alcohol. The chlorosilanes can have a cyano-substituted monovalent hydrocarbon radical substituent. The process is run at pressures below about 200 mm Hg to improve yields of product and reduce by-product formation.
Nitzsche et al., U.S. Pat. No. 3,792,071, issued Feb. 12, 1974, describe an improved continuous process for producing alkoxysilanes in a reactive distillation process where the alcohol reactant is introduced into the column below the introduction point of the halosilane reactant. Temperature in the column is maintained above the boiling point of the alcohol and the product is removed below the point of introduction of the alcohol. Nitzsche et al. teach that the halosilane can be substituted with a .beta.-cyanoethyl radical.
Schinabeck et al., U.S. Pat. No. 4,298,753, issued Nov. 3, 1981, describe a continuous two-stage process for preparing alkoxysilanes. The process comprises introducing in a liquid phase a chlorosilane and a hydroxyl-containing aliphatic compound in parallel flow into a first reactor; then removing the liquid reaction mixture from the first reactor and introducing it at the head of a column used as the second reactor, which is maintained at an elevated temperature, and adding a hydroxyl-containing aliphatic compound as a gas at the lower end of the column. An alkoxysilane product is recovered from the bottom of the column. Schinabeck et al. teach the chlorosilane may be substituted with a .beta.-cyanoethyl radical.
Fischer et al., U.S. Pat. No. 4,506,087, issued Mar. 19, 1985, teach a continuous process for preparation of alkoxysilanes with hydrogen chloride contents of less than 20 ppm. In the described method, the esterification is performed in a reaction vessel and the raw esterification product is continuously removed and delivered to the top of a column. In the column, the reactant alcohol is vaporized and condensed at the top. The raw product drips from the top of the column to the bottom where it is collected. Fischer et al. teach that 2-cyanoethyltrichlorosilane can be a suitable starting compound for their process.
Bank et al., U.S. Pat. No. 4,924,022, issued May 8, 1990, teach a continuous system for the manufacture of organoalkoxysilanes. The reactor consists of a fractionating column that allows for completion of the reaction and separation of the hydrogen chloride formed as a by-product. Bank et al. teach cyanoethyltrimethoxysilane as an example of a product of the reactor.